The present invention relates to a method and an apparatus for decoding video data and video data with audio data.
Recently, with advance of the information processing technology, there has been broadly employed a system in which video and audio are digitized for the recording and reproduction thereof.
It is possible to produce a copy of digital data without deterioration thereof and hence the digital data is suitable for the editing operation. Therefore, there exists a considerable need for an editing system and a search system to process digital video data and digital audio data.
In this operation, to efficiently achieve the editing operation of video and audio, it is essential that data to be recorded can be retrieved at a high speed.
Attention has been consequently attracted to a non-linear editing system using such random-access media for accumulating therein digital data as a magnetic disk, a magneto-optical disk, and an optical disk.
In general, however, the random-access media described above is limited in the capacity thereof.
On the other hand, the digital video data and digital audio data is large in volume. Particularly, the data volume of video data is quite large.
For example, to accumulate digital video data for one hour under a condition that the video data has a speed of 30 frames per second, each frame includes 352 pixels by 240 pixels, and each pixel includes 24 bits, there is required a storage capacity of about 24 gigabytes.
In the non-linear editing system, consequently, the data volume of video is generally reduced using a data compression technology.
For the video data compression in a commercial non-linear editing system, Motion Joint Photographic Experts Group (JPEG) method has been broadly adopted worldwide at present.
The Motion JPEG method is a method of compressing video data using a JPEG method originally developed to compress still video data, and consideration has not been given to audio data. Consequently, the format of video data with audio data varies between editing systems, leading to a problem of compatibility of data.
On the other hand, the MPEG method is an international standard including a method of compression and decompression of video and audio as well as a method of synchronous reproduction of video and audio. Therefore, data conforming to the MPEG method has high data compatibility.
In consequence, when a data is communicated between general users, it is convenient to adopt an editing system utilizing the MPEG method.
Details of the MPEG method has been described in ISO/IEC Standard No. 11172-1 MPEG1 Video, ISO/IEC Standard No. 11172-3, ISO/IEC Standard No. 13818-1 MPEG Video, and ISO/IEC Standard No. 13818-3.
In an operation to edit video and/or video with audio data in which desired scenes are kept retained and undesired scenes are deleted, it is a general practice that the contents of video and/or video with audio data are first confirmed to select the scenes, which however requires quite a large volume of labor.
In this situation, it can be considered that the system for editing video and/or the system for editing video with audio data are/is provided with a function to automatically detect a scene change such that the operation to select/delete scenes is facilitated so as to minimize the volume of labor in the editing operation.
To detect the scene change in the video data compressed in the MPEG method or the like, it will be possible to adopt a method in which the compressed video data is first decoded to attain image data and then a scene change detection processing is accomplished for the image data.
However, the method requires two processings including a decode processing and a scene change detect processing and hence the processing load is heavy and/or overhead is increased.
Consequently, a high processing performance is required for the video editing system in this method, which arises a problem of a high cost due to the high processing performance of the video editing system.
To solve the problem above, the JP-A-6-133305 discloses a technology in which the scene change is detected in accordance with the data volume of each frame of the compressed video data without decoding the compressed video data.
The MPEG method described above includes three kinds of coding methods and the data volume of each frame varies depending on the coding methods.
Consequently, when detecting the scene change according to the data volume of each frame, it is necessary to consider the coding method for each frame.
Moreover, it is a general practice in the MPEG method to control the data volume such that data volume is fixed for each unit of time in the coding operation.
That is, the data volumes respectively of the frames related to the same coding method resultantly take values which are similar to each other.
Therefore, in the method described in the JP-A-6-133305, there is a danger of a wrong scene change detection for the video data in the MPEG format.
Additionally, the method described in the publication of JP-A-6-133305 is attended with a problem that consideration has not been given to audio data.